How do we know we are without excuse before God?

Paul asserts in Romans 1:20 that God's invisible attributes, eternal power, and divine nature are clearly seen through the creation, leaving humankind without excuse for their unbelief. This speaks to the Reformed doctrine of total depravity—though God has made knowledge of Himself available, all have turned away. Every person knows, intuitively in their hearts, the existence of God as evidenced in creation, yet they suppress this truth through unrighteousness. Thus, when they stand before God, they have no legitimate excuse for their rejection of Him.